Near field communication, or NFC, is a set of short-range wireless technologies, typically requiring a distance of 4 cm or less. NFC generally operates at 13.56 MHz and at rates ranging typically from about 106 kbits/s to 848 kbits/s. NFC requires that NFC devices be present within a relatively close proximity to each other so that their corresponding magnetic fields can couple and the devices can exchange information.
An NFC device is required to sense proximity of a target (usually a card) in order to initiate communication. One way to do this is for the NFC device to constantly initiate communications for all possible card types (A, B and F) until it receives a response. This approach has the disadvantage of draining the battery because of the continuous polling (tens of mA).
Therefore, there is a need for a better proximity sensing mechanism for an NFC device that does not drain the battery but can still detect any card which comes within its proximity.